Method of and apparatus for treating waste gas by irradiation with electron beam

ABSTRACT

A method of and apparatus for treating waste gas by irradiation with electron beams wherein an electron beam irradiation chamber for irradiation with electron beams from an electron beam accelerator is provided in the vicinity of a main dust for waste gas; a part of the waste gas to be treated is introduced into the electron beam irradiation chamber where the waste gas is irradiated with electron beams to thereby form active species such as O and OH radicals; the waste gas having the active species formed therein is fed into the waste gas main duct by means of a feeding device; the waste gas fed into the waste gas main duct is dispersed into and mixed with the waste gas flowing through the main duct by means of a dispersing device, thereby changing noxious (gas) ingredients in the waste gas into the form of a mist or dust or the action of the active species; and the mist or dust is captured by means of a capturing device, for example, a dust collector.

TECHNICAL FIELD

The present invention relates to a method of and apparatus for treatingwaste gas wherein waste gas containing noxious (gas) ingredients such asSO₂ and NO_(x) is irradiated with electron beams to change the noxious(gas) ingredients into the form of mist (sulfuric acid and/or nitricacid) or dust (ammonium sulfate and/or ammonium nitrate) and theresulting mist or dust is then captured with a dust collector or thelike.

BACKGROUND ART

One method of waste gas treatment whereby noxious (gas) ingredients suchas SO₂ and NO_(x) are removed from waste gases is a method wherein wastegas is irradiated with electron beams to form various active speciessuch as O and OH radicals from oxygen, water, etc. in the waste gas sothat the active species act on the noxious (gas) ingredients in thewaste gas such as to form mist and this mist is further changed intodust in the presence of ammonia or the like, the mist and dust thenbeing captured with a dust collector or the like.

FIG. 1 schematically shows the structure of an electron beam irradiationportion of a waste gas treatment apparatus for carrying out this wastegas treatment method. As illustrated, a waste gas duct 1 is providedwith irradiation windows 2, and waste gas passing through the waste gasduct 1 is directly irradiated with electron beams 4 emitted fromelectron beam accelerators 3 through the irradiation window 2. In thestructure wherein the electron beams 4 are directly applied to theinside of the waste gas duct 1, when the amount of waste gas increasesto that which would be treated in a practical application and the sizeof the waste gas duct 1 increases correspondingly, it has heretoforebeen necessary, in order to allow all of the waste gas to absorb theelectron beams 4, to dispose a multiplicity of electron beamaccelerators 3 (two in the illustrated example) at the outer peripheryof the waste gas duct 1 and also to increase the maximum range of theelectron beams 4, as shown by the chain lines 5. However, disposition ofa multiplicity of electron beam accelerators 3 involves disadvantage inthat the structure of the waste gas treating apparatus becomescomplicated and costs are raised. Further, in order to increase themaximum range of the electron beams 4, it is necessary to raise theacceleration voltage for electron beams, which leads to a substantialrise in the cost of the electron beam accelerators 3. In addition, ifelectron beams are accelerated at high voltages, high-energy X-rays aregenerated and a thick concrete wall or the like must be provided inorder to provide shielding from such high-energy X-rays, which resultsin a rise in the overall cost of the waste gas treatment apparatus.Thus, the prior art suffers from various problems.

It should be noted that there are techniques which aim to have all ofthe waste gas irradiated with electron beams at a uniform dose,including those disclosed in the specifications of Japanese PatentPublic Disclosure Nos. 49-096975 and 55-097232 and U.S. Pat. Nos.4,507,265 and 4,596,642, but none of them completely solves theabove-described problems.

Further, there is a technique disclosed in the specification of JapanesePatent Public Disclosure No. 61-68126 wherein atmospheric air isintroduced into an electron beam irradiation reactor to allow said airto be irradiated with electron beams to thereby form ozone and oxygenatoms therein. Said air having ozone and oxygen atoms is mixed with awaste gas to oxidize NO in the waste gas to form NO₂ and then the wastegas is introduced to a wet absorption tower to effect desulfurizationand denitration.

In the desulfurization and denitration of that technique, since a wetabsorption tower is used the absorbing solution used in the wetabsorption tower contains a large amount of nitrogen and sulfurcompounds which are difficult to treat and costly waste water disposalequipment is therefore needed to treat the absorbing solution. Thisleads to the problem of high costs in the installation and maintenancethereof.

The present invention is directed to solution of the above-describedproblems of the prior art and it is an object of the present inventionto provide a method of and apparatus for treating waste gas byirradiation with electron beams, wherein a part of the waste gas takenfrom the main stream of waste gas is irradiated with electron beamsusing a low-voltage type accelerator to form active species such as Oand OH radicals in the irradiated waste gas and to thereby activate it,the activated waste gas then being uniformly fed into the main stream ofwaste gas and thereby effectively removing noxious gas ingredients suchas SO₂ and NO_(x) from the waste gas.

DISCLOSURE OF INVENTION

To attain the above-described object, the present invention provides awaste gas treatment method which comprises: irradiating a part of thewaste gas which is the object of treatment with electron beams to formactive species such as O and OH radicals in the irradiated waste gas;mixing the waste gas having the active species formed therein with thewaste gas which is the object of treatment, thereby changing the noxious(gas) ingredients in the waste gas to be treated into the form of a mistor dust by the action of the active species; and capturing the mist ordust.

The present invention also provides a waste gas treatment apparatuswhich comprises: an electron beam irradiation chamber for irradiationwith electron beams from an electron beam accelerator; a feeding devicewhich introduces a part of the waste gas to be treated into the electronbeam irradiation chamber where the waste gas is irradiated with electronbeams to thereby form active species such as O and OH radicals, andwhich feeds the waste gas having the active species formed therein to awaste gas main duct through which the waste gas to be treated isflowing; a dispersing device for uniformly dispersing in the waste gasmain duct the waste gas fed thereinto from the feeding device; and acapturing device for capturing noxious (gas) ingredients in the wastegas within the main duct which have been changed into the form of a mistof dust by the action of the active species.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically shows the structure of an electron beam irradiationportion of a conventional waste gas treatment apparatus;

FIG. 2 schematically shows the structure of a waste gas treatmentapparatus for carrying out the waste gas treatment method according tothe present invention;

FIG. 3 is a sectional view taken along the line X--X of FIG. 2;

FIG. 4 schematically shows the structure of another waste gas treatmentapparatus for carrying out the waste gas treatment method according tothe present invention; and

FIG. 5 is a sectional view taken along the line Y--Y of FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Modes for carrying out the present invention will be describedhereinunder with reference to the drawings.

FIG. 2 schematically shows the structure of a waste gas treatmentapparatus for carrying out the waste gas treatment method according tothe present invention, while FIG. 3 is a sectional view taken along theline X--X of FIG. 2.

An electron beam irradiation chamber 8 for irradiation with electronbeams 7 from an electron beam accelerator 6 is disposed in the vicinityof a waste gas main duct 12 through which waste gas 17 flows. Thedistance from the electron beam irradiation opening of the electron beamaccelerator 6 to the wall surface of the electron beam irradiationchamber 8 is set so as to be slightly greater than the maximum range ofthe electron beams 7. One end of the electron beam irradiation chamber 8communicates with a waste gas main duct 12 allowing waste gas 18 toenter irradiation chamber 8, while the other end thereof is communicatedwith a dispersing device 13 set within the main duct 12 through asuction transfer blower 9 and a pipe line 10. The dispersing device 13comprises a plurality of radial tubes 14 disposed so as to extendradially from the central portion of the main duct 12 and concentrictubes 15 disposed concentrically, the radial tubes 14 and the concentrictubes 15 communicating with each other and also communicating with thepipe line 10. Each of the radial and concentric tubes 14 and 15 has amultiplicity of small bores 16 so formed as to face downstream of theflow of waste gas 17. It should be noted that the suction transferblower 9 and the pipe line 10 constitute in combination a feeding devicefor feeding waste gas 18 from the electron beam irradiation chamber 8 tothe dispersing device 13.

By virtue of the above-described arrangement of the waste gas treatmentapparatus, the waste gas 18 sucked into the electron beam irradiationchamber 8 from the waste gas main duct is irradiated with the electronbeams 7 from the electron beam accelerator 6, so that oxygen and waterin the waste gas are formed into active species such as O and OHradicals. The waste gas having the active species formed therein issupplied to the dispersing device 13 through the pipe line 10 by meansof the suction transfer blower 9, and in the dispersing device 13 thewaste gas is uniformly dispersed into and mixed with the waste gas 17within the main duct 12. As a result, the active species such as O andOH radicals act on noxious (gas) ingredients such as SO₂ and NO_(x) inthe waste gas 17 to change such noxious (gas) ingredients into the formof mist (sulfuric acid, nitric acid, etc.). If an appropriate amount ofammonia gas is injected from a part (not shown) of the pipe line 10, themist and the ammonia gas react with each other to form dust (ammoniumsulfate, ammonium nitrate, etc.). By capturing the mist and dust bymeans of a dust collector (not shown) such as an electrostaticprecipitator, a bag filter, an active carbon separator, etc., all ofwhich are conventional, it is possible to remove noxious (gas)ingredients such as SO₂ and NO_(x) from the waste gas 17.

FIG. 4 schematically shows the structure of another waste gas treatmentapparatus for carrying out the waste gas treatment method according tothe present invention, while FIG. 5 is a sectional view taken along theline Y--Y of FIG. 4.

An electron beam irradiation chamber 21 is disposed in the vicinity of awaste gas main duct 23. One end of the electron beam irradiation chamber21 is communicated with the waste gas main duct 23 through a pipe line22, while the other end thereof is communicated with a dispersing device27 through a suction transfer blower 24, as pipe line 25 and an annularpassage 26. The electron beam irradiation chamber 21 is provided with anelectron beam accelerator 19. The distance from the electron beamirradiation opening of the electron beam accelerator 19 to the wallsurface of the electron beam irradiation chamber 21 is set so as to beslightly greater than the maximum range of electron beams 20.

The dispersing device 27 comprises a plurality of fins 28 thatcommunicate with the annular passage 26 and blades 29 which are sodisposed as to face the fins 28 and which rotate in the direction of thearrow 30. Each fin 28 has a multiplicity of small bores 31 formed in thereverse side thereof as viewed from the direction of the arrow 30, sothat the vortex of waste gas 32 caused by the rotation of the blades 29allows the waste gas irradiated with electron beams and delivered fromthe electron beam irradiation chamber 21 to be uniformly dispersed intoand mixed with the waste gas 32. It should be noted that, in thefigures, the reference numeral 33 denotes a motor for rotating theblades 29, while the numeral 34 denotes a support member for supportingthe motor 33 within the waste gas main duct 23.

It should be noted that although in the above-described example theblades 29 are rotated by the motor 33, the arrangement may, of course,be such that the driving section, for example, a motor, for rotating theblades 29 is provided outside the waste gas main duct 23 and therotational force from the driving section is transmitted by appropriaterotational force transmission menas, for example, gears, chain or belt.

By virtue of the above-described arrangement of the waste gas treatmentapparatus, a part of the waste gas sucked in form the waste gas mainduct 23 through the pipe line 22 is irradiated with the electron beams20 from the electron beam accelerator 19, so that oxygen and water inthe waste gas are formed into active species such as O and OH radicalsin completely the same way as in the above-described example (theexample shown in FIG. 2). The waste gas having the active species formedtherein is dispersed into and mixed with the waste gas 32 in the wastegas main duct 23 through the dispersing device 27. As a result, theactive species act on noxious (gas) ingredients in the waste gas 32 toform mist or dust. Thus it is possible to capture the mist or dust bymeans of a dust collector such as an electrostatic precipitator, a bagfilter, an active carbon separator, etc., all of which are conventional.

It should be noted that the structures of the waste gas treatmentapparatus shown in FIGS. 2 to 5 are one embodiment of the presentinvention and that the present invention is not necessarily limitedthereto. In short, each section of the waste gas treatment apparatus mayhave any specific disposition and structure, provided that the apparatusis arranged such that an electron beam irradiation chamber forirradiation with electron beams from an electron beam accelerator isprovided in the vicinity of a main duct for waste gas: a part of thewaste gas to be treated is introduced into the electron beam irradiationchamber where waste gas is irradiated with electron beams to therebyform active species such as O and OH radicals; the waste gas having theactive species formed therein is fed into the waste gas main duct bymeans of a feeding device; the waste gas fed into the waste gas mainduct is dispersed into and mixed with the waste gas flowing through themain duct by means of a dispersing device, thereby changing noxious(gas) ingredients in the waste gas into the form of a mist or dust bythe action of the active species; and the mist or dust is captured bymeans of a capturing device a duct collector such as an electrostaticprecipitator, a bag filter, an active carbon separator, etc., all ofwhich are conventional.

As has been described above, according to the present invention, a partof a waste gas is taken and irradiated with electron beams to formactive species in the waste gas to thereby activate it, and theactivated waste gas is then mixed with the gas which is object oftreatment, thereby changing noxious (gas) ingredients in the waste gasinto the form of a mist or dust. Therefore, it is unnecessary todirectly irradiate all of the waste gas as in the prior art, and even ifthe amount of waste gas increases to the extend that would be expectedif the treatment is applied on a practical scale and the size of thewaste gas duct increases correspondingly, it is unnecessary to dispose amultiplicity of electron beam accelerators and raise the accelerationvoltage. Accordingly, it is possible to markedly lower the installationcost of an electron beam accelerator and peripheral devices. Forexample, in the conventional arrangement wherein electron beams aredirectly applied to waste gas, it has heretofore been necessary to setthe acceleration voltage of the electron beam accelerators at a highlevel, i.e., 800 kV or 1,000 kV, in order to obtain satisfactoryelectron beam energy in relation to the waste gas duct size or the likefor the purpose of uniformly forming active species in the waste gas,whereas, in the case of the present invention, an electron beamaccelerator with an acceleration voltage of about 300 kV suffices and itis therefore possible to markedly lower the installation cost of theelectron beam accelerator and peripheral devices.

Further, a method of and apparatus for treating waste gas by irradiationwith electron beams according to the subject invention is one whereinthe noxious ingredients in the waste gas are changed into the form of amist or dust by the action of the active species (O and OH radicals,etc.) and the mist or dust is captured by means of a conventionalcapturing device. Accordingly, this invention differs from the case ofusing a wet absorption tower as described which requires treatment ofthe waste water emanating from the absorbing solution used in the wetabsorption tower, allowing the costs of installation and maintenance tothus be lowered in this invention.

Furthermore, in the present invention, since a part of the waste gas istaken and irradiated with electron beams, there is no increase in thevolume of waste gas even when the waste gas irradiated with electronbeams is mixed with the waste gas flowing through the main duct,compared with the case wherein air which is externally taken in isirradiated with electron beams. Thus this invention has no necessity fora large-capacity blower.

INDUSTRIAL APPLICABILITY

Thus, in the method of and apparatus for treating waste gas byirradiation with electron beams according to the present invention,noxious (gas) ingredients such as SO₂ and NO_(x) in waste gas arechanged into the form of a mist (sulfuric acid and/or nitric acid) ordust (ammonium sulfate and/or ammonium nitrate) and the resulting mistor dust is then captured with a dust collector or the like. Accordingly,the method and apparatus of the invention are suitable for utilizationas a method and apparatus for treating waste gas such as boilercombustion waste gas in thermoelectric powder plants that use fossilfuels, for example, heavy oil or coal, as a fuel or sintering waste gasin iron works.

What is claimed is:
 1. A method of treating waste gas flowing in a waste gas main duct, comprising:diverting a part of said waste gas flowing in said main duct from an outlet of said main duct to an electron beam irradiation chamber exterior to said main duct; irradiating said part of the waste gas to be treated with electron beams in said irradiation chamber exterior to said waste gas main duct to form active species in the irradiated waste gas; introducing into said waste gas main duct downstream of said outlet the waste gas having said active species formed therein and mixing the introduced waste gas having said active species formed therein with said waste gas to be treated, thereby changing noxious (gas) ingredients in said waste gas to be treated into the form of a mist or dust by the action of said active species; and capturing said mist or dust.
 2. An apparatus for treating waste gas flowing in a waste gas main duct, comprising:an electron beam irradiation chamber located exterior to said waste gas main duct for irradiation of any waste gas within said chamber with electron beams from an electron beam accelerator; a feeding device having an inlet coupled to an outlet of said main duct and which introduces a part of waste gas to be treated into said electron beam irradiation chamber where said part of said waste gas is irradiated with electron beams thereby to form active species and which feeds the waste gas having said active species formed therein to an inlet of said main duct downstream of said outlet of said main duct; a dispersing device disposed in said main duct and coupled to said inlet of said main duct for uniformly dispersing in the main duct downstream of said outlet the waste gas having said active species fed from said feeding device; and a capturing device for capturing noxious (gas) ingredients in the waste gas within the main duct which have been changed into the form of a mist or dust by the action of said active species. 